poj 1942 Paths on a Grid

#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>using namespace std;long long n, m;long long com(long long n, long long r){    if (n - r < r)        r = n - r;    long long i, j, s = 1;    for (i = 0, j = 1; i < r; i++)    {        s *= (n - i);        for (; j <=r && s %j == 0; ++j) s /=j;    }    return s;}int main(){    while (scanf("%lld%lld", &n, &m), n | m)        printf("%lldn", com(n + m, n));    return 0;}